Pressure is not only an important extensive variable in physicochemical and thermodynamics investigation of matter, but also is an essential process parameter in certain specialized technologies which utilize a high pressure route for manufacturing a final product. In recent years, extensive efforts have been devoted to the measurement and standardization of high pressure environments (for example, "Accurate Characterization of the High Pressure Environment", editor E. C. Loyd, National Bureau of Standards, Special Publication 326, 1971). In the range from approximately 10 kbar to 300 kbar, a series of reference points--the so-called "fixed points"--indicated by phase changes and/or resistance jumps in selected materials are commonly used for pressure calibration as well as sensing. In the range below 10 kbar, that is, 0.5 kbar to 10 kbar, however, such fixed points calibrants are rare, for example, Ce at 7 kbar and the Hg freezing point at 0.degree. C., 7.6 kbar. Manganin (84 Cu-12 Mn-4 Ni) gauges are often used in the pressure range from 2 kbar to 14 kbar and higher, but this material is rather insensitive having a pressure coefficient of electrical resistance EQU k=(R/R.sub.o)1/P
(where R.sub.o is the resistance at atmospheric pressure) which is on the order of 10.sup.-3 per kbar and is not constant.
Recently, non-ohmic ceramics based on ZnO have been utilized for surge protection against transient voltage and power overload. Zinc oxide based metal oxide varistors of the bulk type are, for example, described in U.S. Pat. Nos. 3,663,458 and 3,682,841, which patents are incorporated herein as background material. Prior art investigations of the properties of the metal oxide varistor materials have been performed at atmospheric pressure.